Furnace blowing fuses

[hlozano]

It's that time of year when we go on our first outing for the year. Took the cover off our Reflection 317RST and started going through my normal checks. Since it still gets down in the 30's here in Ohio this time of year, the furnace is one of the first things I check. After bleeding the LP which consists of firing up the stove and leaving it on for a couple minutes, I proceeded to kick on the furnace. The furnace started it's pre-purge cycle then nothing. It never gets to a point where the igniter tries to ignite. It turns out I blew the 15A fuse, so I replace it and try again. Same thing, blown fuse. I checked to make sure I wasn't getting continuity to ground at the fuse connection which tells me the circuit isn't shorted. It can't be the reset switch because I'm reading 12volts with a good fuse. So I'm thinking control board since I had problems with it last year. (I had a problem with the control board last year. I basically had to solder a new jumper because of Atwoods poor design and placement which allowed the control board to sit in water.)

I ordered a new control board from Amazon and installed it, fingers crossed, turn on the heat and same thing, blown fuse. Now I'm scratching my head! I decide to throw in a 35A fuse just to see if the furnace would fire. To my surprise the furnace fired right up. I only let it run for a couple minutes then shut if off because I didn't want to damage anything with the larger fuse. I then put a 15A fuse back in and turned the furnace back on and again it fired right up. I set the thermostat to 68 and continued to let it run waiting for it to cycle off. After about 20 minutes it was getting pretty toasty in the coach yet the furnace continued to run. I grabbed my temp gun and pointed it at the thermostat and got a reading of 71 degrees. I ended up lowering the temp setting on the thermostat down to 64 before the furnace finally cycled off.

My theory on the blown fuses is the blower may have been seized a little from sitting all winter causing a higher start up amp draw. Someone please chime in if I'm wrong in my though process. As for the furnace not cycling off, my wife swears in the past she's shedding down to a T-shirt before the furnace finally kicks off. Is there anything I can do to calibrate the thermostat is that just the norm?

[hlozano]

Mr RV Works has excellent videos and tutorials tearing into these furnaces. Just thought I'd share for those that need help identifying parts and dissassembly.

https://www.youtube.com/watch?v=oaTW0oNf6Qw

[azrving]

Id bet on the motor being lazy after sitting. Depending on the thermostat it may have anticipate settings. My cheap home thermostat for electric heat has a deeper menu that lets me go in and set how many times per hour it will come on. Older therms had small arms/dials to adjust the spread of when it turns off and back on.

[hlozano]

Thank you both for your input. I want to add that I did reach up and rotate the blower and it seemed like it spun freely before trying the 35A fuse. I'll have to look at the model number of the furnace and call Dometic about the relocation kit. I'll also look at replacing the thermostat. This is the thermostat I currently have in my unit. https://www.etrailer.com/Accessories-and-Parts/Atwood/AT15029.html

Finally, I tear into the limit switch and check the wiring. I'm not sure where that guy is located but there's enough youtube videos out there to hopefully point me in the right direction.

[dougrainer]

I would verify the Hi limit switch wires are not touching the burner chamber. Sail Switch will not blow a fuse. Running on a 35 amp fuse allowed the system to come on and heat just enough to allow a burned wire insulation to drop off the chamber. Also. Atwood has a TSB for the relocation of the control modules to prevent water intrusion damage. On Certain models. If you had a motor problem, you would have heard it making weird loud noises. Doug

[opnspaces]

My first thought was the sail switch is sticky. But now that it's running on the 15A fuse I would guess the grease on the furnace motor is dried up. You'll probably have to replace the motor in the end to get it working.

Is there a name and model number on the thermostat? Does the thermostat control both the heat and AC, or just the heat? You should be able to pull the cover off and see if there is any obvious adjustment. But it sounds like the thermostat is acting up and I would just replace it. You can buy an inexpensive digital thermostat to replace the original. I bought mine for $25 from Walmart. If you go this route just make sure the thermostat can run off batteries and supports a 24v system. The swap for me was easy. It took more time drilling two holes in the wall than it took to wire it up.